Charlottesville Area Masters of Real Ale

So I just got my new kettle today and brewed its inaugural batch.  Wow, its a cool kettle, but I am going to need to make some serious process adjustments for it.  For those who are interested, here are a couple:

- Evaporation Rate - Greg warned me of this, as he has the same kettle, but my evaporation rate increased dramatically.  I figured I would be ok with a pre-boil volume of 8 gallons for my Dogfish Head 90 min clone (I am making it with the Starr Hill Chico yeast, yay!).  Granted it is a 1 hour and 45 min boil, but WOW.  I ended up with under 5 gallons of wort and the end of the boil, and even less when you account for trub and all the hops.  I was not even boiling at full heat.

- Chiller - My current immersion chiller is built for the old pot, thus it is tall and narrow.  Now it needs to be bigger in diameter and shorter.  Things actually cooled down quickly, but that was because it was 20 outside when I was done and the cold water temp is just above freezing.  The chiller design will not work in the middle of summer.

- Moving the Pot Around - The pot has to weigh almost 30 pounds and it is REALLY heavy half full.  I did get the ported version and ball valve assembly, but I have not worked out how to fit that into my process yet.  I certainly cannot try to lug it around like I did today.


On the positive side, once I get the evaporation rate thing figured out, I can actually hit my target ending volume pretty easily now, as I can boil more wort than I need (my old pot was 7 gallons, and I could never fill it up past 6.25 gallons without a boil over).  Boil overs are also a thing of the past and I can now do an occasional 10 gallon batch.  Yay! 

Me's got a good hook-up for a fat copper coil. I made my own from one: 47' of 1/2" OD copper. Why 47"? Cause I screwed up bending the other 3' and now have lots of little pieces of copper.

I think mine is from 25 feet of copper and I have had it for a few years now.  I think I just need to change how it bends a bit and it may still work.  We will see when it gets to summer time and the tap water is not 35 degrees out of the faucet.  If not, away to Lowes I shall go.

You can get a 50' coil of 1/2" OD from a great supplier via UPS for less than $70. I'll try to remember the website that I got if from.
I think my evaporation rate is 25% per hour at a nice steady rolling boil. 8 gallons down to 6 in an hour. An extra gallon of water is a small price for a super kettle.

I brewed in my converted kegs recently.  I have to say, I'm really pleased with the heat the bayou burner put off, and the 15 ft tall steam column that came out of my kettle.  As for evaporation, do you guys know how much the humidity influences the evaporation rate?  As in, it might change in the summer.  I think I observed about a 25% evaporation rate also.  The last batch I brewed was indoors, and my little place was like a tropical rainforest after I was done because the air was so thoroughly saturated.

I would imagine that relative humidity would change the evaporation rate a good deal, but that is just intuition.  Perhaps a good thing to experiment with.  I definitely need to change the boil rate and start with a higher volume of wort at the start of the boil.  I knew I would have to make some adjustments with the new piece of equipment; that is part of the fun, right?

Yup. I undershot my first brew on the new kettle. Can't say I've made that mistake again although I've wasted countless gallons boiling down to hit my target OG...Que sera, sera. It is a pain though to go to all that work and then end up with less than 5 gallons in the fermenter.

I'm fairly certain there is an inverse relationship between evaporation rates and humidity, but how much descends quickly into messy equations.  I think what is just as important as humidity is temperature.  So the bigger issue is vapor pressure and looking at relative humidity. 

I would think lower evap. rates in the summer.

I'm sure whatever you're driving at is apropos but given the fact that I've been imbibing, I didn't catch a word of that last post!  Too many big words. Or too much Dark Starr Stout for me.

I looked into said messy equations, since I spend all day modeling the brain with math and computer science.

I also spend a lot of time identifying the most influential bit(s) of the system to include in the model (the math is hard enough without including every incomprehensible complexity).

Hypothesis :: The most important factor in evaporation is the quantity of heat that can be imparted into the kettle.  (The other factors have a relatively minor impact.)

Justification :: It dawned on me that every gram of water evaporated from the kettle is removing a significant amount of heat from the kettle.  (the system is not closed.)  Thus, the more heat that can be pumped into the system, the faster the evaporation.  The other factors do /influence/ the evaporation rate, but in an hour?  not much!

Empirical Evidence :: Evaporating water on a stovetop with conventional burners is impressively slower and less vigorous than evaporating water with a monster propane burner.  I could bring 8 gallons of wort to a boil in around an hour (from sparge out ~165F to boiling at ~220F) and evaporate 3 gallons of water in around 2 hours with 3 natural gas burners and 3 kettles (guess 18k-25k BTU per burner) -- (3 total hrs).  With a banjo burner, I can heat 14 gallons of water to boil in an hour and evaporate 4 gallons in 2 hours (2 total hrs).  That's a major difference.  More volume to heat, more water to evaporate and complete in LESS time.  (I have only brewed outdoors when it is cold and the air is dry.)

------------------------------------------------
Kitchen                ||  Banjo Burner
------------------------------------------------
+ more surface area    ||  - less surface area
+ warmer ambient temp  ||  - colder ambient temp
- more humid           ||  + less humid
- less BTU             ||  + more BTU
+ less water to heat   ||  - more water to heat
================================================
                     RESULT
================================================
- slower evaporation   ||  + faster evaporation
- anemic boil          ||  + vigorous boil
------------------------------------------------

This is all qualitative theory, and I've got no quantitative results to back me up, but I'm pretty sure I'm right.

That makes sense, Hoptical.  I would also add that the shape of your kettle makes a difference in the evaporation rate.  The more shallow the pot is, assuming the volume of water is the same, the larger the evaporation rate will be.  I would guess that there is a larger surface area of the water that exchanges with the air, thus losing the water vapor.  I have definately seen this to be true on the three different pots I have used in my brewing career.

I believe that.  It's worth trying to empirically rank the effects of equipment on the rate of evaporation.  The world is complicated.

I broke in the keggle this weekend with a garden variety west coast IPA.  I'm still working out the details, but it is interesting to see the differences between my old 7 gallon aluminum pot and this 15 gallon SS keggle.

Interestingly, the keggle seemed to heat up faster than the aluminum (perhaps because it sits lower and closer to the flame) but it also seemed to lose heat faster.  (Perhaps the surface area that is in contact with the outside air and the metal's properties.)

Evaporation was higher, but not as high as I expected.  The keggle was recently welded and I turned around and brewed with it hours later after a quick hydrostatic test.  A more formal testing needs to happen, and I need to ice everything down for calibration as well.

Post some pictures of the new kettle, Jamey.  I would be interested to see how you got it all to work.